The present invention concerns an articulated bus, in particular of the type with a low floor, whereby said bus has a pulling vehicle, a pulled vehicle and an articulated mechanism which connects both vehicles to one another and which contains a rotary junction with a lower part which is connected to the pulling vehicle and an upper part mounted thereupon in a rotating manner around an upward axis of rotation to which the pulled vehicle is connected, whereby the connection between either of these parts of the rotary junction and the accompanying vehicle is a hinged joint with an axis which is diagonal to the rotary shaft of the rotary junction.
In known articulated buses of the above-mentioned type, the hinged joint between one of the vehicles and one of the parts of the rotary junction consists of a rigid structure which forms a whole with the vehicle frame and which is connected in a hinged manner with two protruding parts on either side of the rotary shaft to the above-mentioned part of the rotary junction. Such buses are described among others in patents BE-A-872.030 and NL-A-78 11 557.
When the bus drives on a bumpy road, with two road surfaces which are turned in relation to one another, large torques will arise at the height of the articulated mechanism in the structures of the vehicles with such a hinged joint. These torques, which may be very large, can be absorbed in an articulated bus with an ordinary high floor since there is enough room to make the vehicle frames sufficiently strong. In articulated buses with low floors, however, the structural height of the frame or chassis is too limited to absorb such possible torques.
The invention aims to provide an articulated bus whereby torques in the frames at the height of the articulated mechanism are restricted or avoided, such that it is not necessary to make the frame of the vehicles heavier to this aim, and whereby the hinged joint can be made very simple and especially very compact, all this such that, if required, the floor height of the articulated bus can be kept relatively low without any problems.
This aim is realized according to the invention as the hinged joint between a vehicle and either of the parts of the rotary junction contains two flexible supporting arms, which are situated on either side of the rotary shaft of the rotary junction, and which are each fixed to an end of the vehicle on the one hand, and which are connected in a hinged manner to the part of the rotary junction on the other hand
The flexible supporting arms will be able to reduce any possible torques to an acceptable level thanks to a limited and controlled elastic deformation. These supporting arms form a simple, self-supporting construction which requires only a limited overall height and thus is especially suited to be applied in a low articulated mechanism as is required in an articulated bus with an extremely low floor. The flexible arms are significantly lighter than the conventional rigid constructions which are used instead. Moreover, these flexible arms provide for a significant vibration isolation, which results in more driving comfort for the passenger on bumpy roads.
According to a special embodiment of the invention, the vehicle which is attached in a hinged manner with either of the parts of the rotary junction is the pulled vehicle.
The lower part of the rotary junction is then preferably fixed in a rigid manner to a backward directed protrusion of the frame of the pulling vehicle, whereas the upper part of the rotary junction is fixed in a hinged manner on both sides of the rotary shaft to an end of a flexible arm which is fixed on the front end of the frame of the pulled vehicle.
Practically, the two flexible arms have the shape of parabolic springs.
As already mentioned, the invention is particularly practical for buses with low floors, in particular for such buses whereby the floor of the pulling vehicle and the pulled vehicle are kept at approximately the same level in relation to the ground.
Buses with low floors have been recently developed and are specially built to provide access to disabled and handicapped persons sitting in a wheelchair. In such buses, there are no steps at the door. Moreover, the low floor with low step is usually combined with an extra "kneeling" of the bus at critical bus stops, whereby by means of the pneumatic suspension the superstructure with the floor is lowered in relation to the street or pavement.
New safety problems and problems of structural strength arise with such buses with low floors. Especially the free distance to the road surface at the bottom of the articulated mechanism is critically restricted here on roads with significant slope variations.
With the bus according to the invention, the overall height for building in the articulated mechanism can be limited, such that, taking into account that there should remain a distance of some 200 mm under the articulated mechanism, the floor can be situated at maximum 440 mm above the articulated mechanism. As a result, the floor can be kept at a height of maximum 330 mm above the ground floor over the entire length of the vehicles. The small difference in floor height between the doors and the intermediate floor above the articulated mechanism can be absorbed by means of a slight floor inclination of maximum 6.5%.
In the known articulated buses with a normal floor height, the available overall volumes with the articulated mechanisms are much higher, so that other mechanisms can be used here.
In the articulated buses with low floors, the frame or chassis structure is restricted to the minimum because of the extremely low floor, such that also the structural strength is restricted to the minimum. The two flexible supporting arms which are applied according to the invention are simple, self-supporting constructions which are relatively light and do not require much overall height.
The invention is applicable for articulated buses in which the shaft of the pulled vehicle consists of a rigid shaft, but it is especially useful for articulated buses whereby the wheels of the shaft of the pulled vehicle are steered. With these latter buses, when taking a bend, the pulled vehicle slays more or less in the same path as the pulling vehicle, as a result of which any danger for oncoming traffic is significantly reduced and the outer turning radius of the vehicle is restricted.
According to a preferred embodiment of the invention, the two flexible supporting arms are fixed to the frame of the accompanying vehicle as they are attached between two clamping pieces situated on top of one another which are fixed on top of a part of the frame by means of bolt connections.
By means of shims of varying heights which are placed under the flexible supporting arm, the height between the two vehicles can be adjusted, and the necessary production tolerances can be absorbed.